ABSTRACT/PROJECT SUMMARY Maternal ADHD, present in 25-50% of families of children with ADHD and frequently untreated, interferes with effective parenting and predicts poor child developmental and behavioral treatment outcomes. Based on the literature and our own pilot data, we will randomly assign mothers with ADHD and their young at-risk children to one of two conditions: (1) stimulant medication for mothers with ADHD followed by a child treatment strategy (CTS) beginning with behavioral parent training (BPT) with the added recommendation of child stimulant treatment if the child remains impaired or (2) a CTS without treatment for maternal ADHD on parent, child, and family outcomes. We will examine target mechanisms including improvements in maternal ADHD-related impairment and symptomatology (attention, impulsivity, emotional regulation), parenting skills, and BPT engagement, as well as treatment moderators (baseline maternal ADHD severity, maternal impairment, and parenting skills). Moreover, in an effort to develop a model of treatment that has potential for widespread dissemination while also reducing barriers to receiving care, we will screen mothers for ADHD in primary care, where child ADHD is most often identified and treated, and co-located mental health providers will deliver treatments via telehealth. Development of an implementation plan and associated toolkit using a stakeholder participatory strategy will enhance the ability to move efficiently to adoption of this approach. In addition, we will study the care delivery context, assessing procedures for and rates of screening and participation as well as staffing, workflow, provider- and patient-level acceptability, readiness, and feasibility of implementation approaches. This hybrid effectiveness-implementation project will be achieved via a collaborative R01 across 2 research sites in the US (N = 240 families), with 4-5 primary care partners at each site.